Mitochondria

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Mitochondria

• 0.5-1.0 microns wide,up to 10 microns long
• The long squiggly threads are mitochondria in
  this phase microscopy image

2

• Two membranes
• Outer membrane
• Inner membrane folded
• called cristae

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Mitochondrial function

• Oxidative phosphorylation
• the process by which the enzymatic oxidation of
  cell metabolites is converted into ATP
• Uses electrons from biochemical reactions
• Occurs in a membrane bound electron transport
  system
• Needs ATP-synthetase
• Uses H gradient to generate ATP

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Replication

• Mitochondrial replicate by simple fission

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Variant appearances

• Cristae differ in length, shape and number
  depending on the cells energy needs
• Most cells cristae go halfway across mit.
• Short cristae represent low energy requirements
• Muscle cells cristae cross all of the way
• Muscle cells also have tightly packed cristae
• More cristae represent high energy requirements

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configurations
Orthodox--low level of oxidative phosphorylation
Condensed--high level of oxidative
phosphorylation
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Variations, continued

• Most cristae are arranged in shelves
• In steroid secreting cells, the cristae are
  tubular

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Typical mitochondria Shelf cristae Halfway
through the organelle
Active mitochondria Tightly packed shelf
cristae Crosses organelle
Steroid secreting cell mitochondria Tubular or
circular cristae
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Longitudinal section

• Mitochondria in dendrite
• Up to 25mm

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Matrix Granules

• Are accumulations of calcium phosphate
• Helps maintain low levels of calcium ions in the
  cytosol

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Mitochondrial occurrence

• All cells have some mitochondria
• Most mitochondria situated close to parts of cell
  that have highest energy requirements
• Fewer mitochondria are found in cells that
  operate under anaerobic conditions
• Certain muscle and blood cells

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Abundant mitochondria

• More mitochondria are found in cells that
• have motile machinery
• sequester low pH substances
• pump large amounts of ions
• Small lymphocytes have a few while hepatocytes
  have about 1000

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Cells marked by low s of mitochondria

• Skin epithelia (stratified squamous keratinizing
  epithelia)
• Especially those that are no longer dividing
• Protective function

• Type II skeletal muscle fiber
• white fiber
• Fast twitch
• Works under anaerobic conditions (glycolysis)

FH 6.13a
FH 9.4a
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Low s mitochondria, contd

• Neutrophil
• Glycogen is broken down to yield energy via the
  glycolytic pathway of glucose oxidation
• Citric acid cycle less important
• They have lysosomes, BUT...
• Surviving anaerobically is advantageous since
  they can kill bacteria and clean debris in poorly
  oxygenated areas
• Inflamed or necrotic tissue

FH 3.4a
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Hepatocyte
High number of mitochondria

• A cell with just about every organelle in
  abundance
• Very metabolically active cell
• Detoxifies, produces bile

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Cardiac Muscle

• Continuous contraction requires a lot of ATP

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Skeletal Muscle

• High energy requirement
• Especially the red fibers

Stain for succinate dehyrdgogenase
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Parietal cell of the stomach
Fried egg appearance

• Produces the HCl of the stomach
• In the epithelia lining
• These are the cells targeted by Pepcid AC,
  Tagamet and Zantac-
• indirectly
• Mitochondria are needed to sequester the H

FH 14.12
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Ciliated cells

• ATP is needed to move the microtubules in the
  cilia
• Cilia helps move mucus along in the lumen of the
  trachea and the ovum in the oviduct

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Presynaptic terminal of neuron

• Vesicles contain neurotransmitters
• Mitochondria furnish energy for synaptic activity

FH 7.10 and 7.12
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Tail of sperm

• Flagellum has same microtubule arrangement as
  cilia
• Requires ATP to move
• Mitochondrial inheritance of defects is maternal
  because few, if any, mitochondria enter the ovum
  with the sperm head.

FH 18.7
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Cells of proximal convoluted tubule

• Kidney filtration
• Sodium ions diffuse passively through apical
  membrane
• Ions actively transported out of the cells by a
  sodium/potassium ATPase located in the basement
  membrane
• These cells also provide for protein digestion

An epithelial cell Of the kidney pct
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FH 16.4
FH 16.15d
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Brown adipose
Sympathetic nerve ending

• Heat production is increased in this tissue
  because mitochondria in these cells have a
  transmembrane protein called thermogenin in their
  inner membrane
• Energy is dissipated by heat and warms blood in
  nearby capillaries

FH 4.13d
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Cortisol secreting cell of adrenal cortex

• Mitochondria convert cholesterol into
  pregnenolone which is converted into steroids in
  the sER

FH 17.16
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Rods and Cones of the eye

• The visual process requires a lot of energy
• Protein synthesis and energy conduction

cone
lipofuscin
FH 24.7b
Pigment cell
Rod Cone
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Mitochondrial disease

• Can affect any cells with large numbers of
  mitochondria
• Swelling of mitochondrial matrix
• Caused by DNA mutations or defects that occur in
  the mitochondria or cell nucleus
• Or can be caused by environmental toxicity

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Cell injury

• Can see vacuolated mitochondria
• Result of accumulation of electrolytes and water
  due to damage to the enzymes of the sodium pump.
• First ultrastructural evidence of sub-lethal
  damage is swelling of membrane bound organelles
  (mitochondria and ER)
• Further insult will lead to destruction of the
  cristae.
• When ATP production becomes insufficient to
  maintain other cellular functions, the cell dies

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Vacuolated mitochondria in cell injury
Renal tubular epithelia cell damaged by hypoxia